The most common and most likely answer to this crossword clue is the 7 letter word ACCRUES
I've seen this crossword clue in The Times
A
C
C
R
U
E
S
Buddy explains!
The straight part
We know that "comes as an added extra" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case comes as an added extra = accrues.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does ACCRUES mean?
ACCRUES noun- Something that accrues; advantage accruing
- To increase, to rise
- To reach or come to by way of increase; to arise or spring up because of growth or result, especially as the produce of money lent.
- To be incurred as a result of the passage of time.
- To accumulate
- To become an enforceable and permanent right.